In this pilot study, we propose a two-arm primary prevention trial to test the efficacy of an environmental approach for the prevention of obesity in children who are in the second through sixth grades. An attention-placebo control group will receive an environmental approach for the prevention of alcohol drug tobacco use and abuse. This test of an environmental approach targets a school system for change. Four schools with a total of approximately 1,040 students will be the participants in the study. The four schools will be randomly assigned to one of the two treatment arms. The prevention study will be conducted across two consecutive academic years. The primary endpoint will be body mass index. The primary aim of the study is to test the efficacy of the obesity program for the prevention of weight gain in children. Changes in dietary intake and physical activity will be tested as mediators of changes in body mass index. Also, age of the child, initial body mass index, and gender will be tested as factors that are associated with differential outcomes related to the prevention of weight gain. Secondary endpoints include: body composition, waist circumference, physical activity, dietary intake, body image, mood, and self-esteem. The environmental program for the prevention of obesity will have multiple components that are designed to alter automatic/habitual decision making by students. The results of this pilot study will guide the development of full-scale investigations in a larger set of schools. The findings of the study will have significant impact upon public health policy regarding prevention of obesity. Several innovations are utilized in the study, including novel applications of the internet to provide environmental prompts to parents and families, and the use of a new method, called digital photography of foods, for measurement of the food selections and food intake of individual students, in school cafeterias.